The present invention relates to the extraction of oil from wells, and particularly to the use of ultrasonic energy to assist secondary recovery of oil from wells.
During the extraction of oil from a well, a time is reached at which the production from the well decreases to an uneconomically low value. This occurs because the quantity of oil remaining in the well is reduced, the remaining oil has a relatively high viscosity, and the pressure in the well has decreased to a low value.
In order to increase production of the remaining oil, or to perform "secondary recovery", various techniques have been proposed. One of these techniques involves exposure of the remaining oil to ultrasonic energy, which has been found to create a temporary reduction in the viscosity of the oil. In order to employ this technique on a practical level, it has been proposed to dispose an electroacoustic transducer element in the region of an oil producing formation of an oil well and to supply the transducer with alternating current at a suitable frequency. One such arrangement is disclosed in U.S. Pat. No. 3,322,196, which describes arrangements in which an oscillator and amplifier and associated electrical components for producing the electrical signal are disposed within the well in close proximity to the transducer element.
The reason for disposing the electrical components in proximity to the transducer element is to prevent unacceptably high electrical losses between the power generating components and the transducer itself.
In general, it is considered necessary to connect a power supply to an electroacoustic transducer element by a cable having a relatively short length. For example, a known device for reducing the viscosity of liquids in laboratory and industrial applications is specified to be usable with a cable having a length not exceeding 19 feet.
However, the use of such an arrangement in an oil well has been found to present a number of drawbacks. Thus, for example, all of the electrical components are relatively bulky so that difficulties are encountered in mounting these components for introduction into the well. Moreover, because of the high temperatures which exist within a well having any significant depth, various components of the electrical system will fail after a short period of time.